With the progressive proliferation of information communication equipment such as wireless terminals, the range of frequencies used for communication is broadening, spanning from hundreds of megahertz for a cellular phone, and the like, to gigahertz for a wireless LAN, and the like. Currently, terminals complying with respective communications schemes are independently used. However, for the future, desire exists for a compact terminal which complies with various communication schemes by use of a single wireless terminal. Against the backdrop of an increase in the number of passive components, such as switches to be incorporated into a housing of a terminal, a desire exists for miniaturization of the passive components.
In view of this situation, research and development of an RF-MEMS switch manufactured by the MEMS (Micro Electro Mechanical Systems) technique has become brisk. The RF-MEMS switch is a switch which mechanically switches a signal transmission path by means of actuating a micro-movable electrode. The advantage of this switch is compactness of the device and superior high-frequency characteristics such as an ultra-low loss and high isolation. Moreover, the switch can be manufactured in a process compatible with an RF-IC and, hence, can be incorporated into the RF-IC, as well. Thus, employment of the switch is expected to contribute greatly to miniaturization of a wireless section.
The related RF-MEMS switch is a mechanical switch which switches a signal transmission path by means of: supporting both ends of a membrane-like or rod-like movable element or supporting the movable element in a cantilever fashion; and bringing the movable element into or out of contact with an electrode. Many RF-MEMS switches adopt electrostatic force as the source of driving force for a membrane or a movable element (Patent Document 1). In addition, RF-MEMS switches adopting magnetic force have also been released (Non-Patent Document 2).
A related minute switch of the order of hundreds of micrometers is described in Non-Patent Document 1. In this switch, a signal line through which a high-frequency signal is to be transmitted is formed on a membrane, and a control electrode is provided immediately below the signal line. When a DC potential is applied to the control electrode, the membrane is attracted and bent toward the control electrode by means of electrostatic potential, to thus contact a ground electrode formed on a substrate. As a result, the signal line formed on the membrane enters a short-circuited state, whereby the signal flowing through the signal line is attenuated and interrupted. In contrast, when the DC potential is not applied to the control electrode, the membrane is not bent, and the signal flowing through the signal line on the membrane passes through the switch without being subjected to losses produced by the ground electrode.
Research and development of the RF-MEMS switch originated with one intended for use in military and aerospace applications, and the focus of research and development has been placed on improving signal transmission characteristics. However, when the RF-MEMS switch finds its application in consumer products, such as a portable information terminal and the like, there is sought an RF-MEMS switch which simultaneously satisfies various characteristics such as reliability, durability, high-speed response, low power consumption, a lower drive voltage, miniaturization, and the like, as well as enhanced signal transmission characteristics.
Patent Document 1: U.S. Pat. No. 6,307,452B1
Non-Patent Document 1: J. B. Muldavin and G. M. Rebeiz, IEEE Microwave Wireless Compon. Lett., vol. 11, pp. 334-336, August 2001.
Non-Patent Document 2: M. Ruan, J. Shen and C. B. Wheeler, IEEE Journal of Micro Electromechanical Systems, vol. 10, pp. 511-517, December 2001.